Is the kennedy assassination a closed issue? did Oswald definitely act alone on that day in Dallas? are the versions that question Oswald's sole culpability valid? I ask because even public museums, such as the Sixth Floor Museum (which is the main museum dealing with the facts surrounding Kennedy's death) have given publicity to voices advocating a different story, and in lectures, the same museum staff refers to the Kennedy assassination as a maze. The latter gives me the impression that kennedy's death is still a controversial fact for even the most serious institutions. how do historians deal with this?
There are still plenty of people who would LOVE to sell doubt on the subject. But, really, there's isn't any to speak of. Oswald, who is known to associates as an angry man, is seen going into the Book Depository, where he worked, with an oblong bundle shortly before the motorcade. Right after the assassination, the Carcano rifle is found upstairs, fired, with his fingerprints on it. Oswald himself runs from the scene, kills a policeman who he thinks might get in his way. A photo is found in his possessions of him holding the rifle. The receipt of Oswald's purchase of the rifle is also found. The bullets found in JFK were found to have been fired from the rifle. What more could any jury want?
In a previous answer to the question of why people persist in doubting this extremely explainable event, I wrote ( I've tidied this a bit)
Because we have a very poor intuitive understanding of probability and chance, conspiracies are very appealing to humans. We have a hard time believing that a significant event happened by chance, not by agency. Before the JFK assassination, there were theories about the attack on Pearl Harbor. And even before: during the Plague of Milan of 1621, a man brushed off a bench with his cloak before sitting down. Immediately, someone claimed he was rubbing it with something carrying the plague, an angry mob assembled and beat him to death. And ( not to cross the 20 Year Rule, here) it was not the last time someone wanted to find human agents responsible for an epidemic.
The conspiracy theorists do tend to have similar problems, however: they will point up a number of coincidences as being , as you say, ridiculous or unbelievable. But they will typically propose an alternative scenario that itself has far more glaring problems- and they will blithely ignore them. So, for example, the Jack Ruby/Mafia theory demands impossibly precise coordination between Ruby and the Dallas Police Dept., allowing him to take his time strolling over from the post office to find Oswald being brought out: and that happening an hour later than had been announced, planned. This is why it's usually far more useful to ignore the demands of such theorists for absolute perfection in the established record, and focus instead on the shoddy alternatives they propose.
Bugliosi, V. (2007). Reclaiming History: The Assassination of President John F. Kennedy (1st ed.). W. W. Norton & Company.
In the late 80s my college professor in American History 1945 to present quoted "The Committee believes, on the basis of the evidence available to it, that President John F. Kennedy was probably assassinated as a result of a conspiracy. The Committee is unable to identify the other gunman or the extent of the conspiracy. "House Select Committee on Assassinations .
To me look at HSCA testimony of “John Scelso,” May 17, 1978 as well, When asked why Harvey might have told his wife to destroy his papers, Whitten’s reply was sardonic and telling.“He was too young to have assassinated McKinley and Lincoln,” Whitten said. “It could have been anything.https://jfkfacts.org/bill-harvey-armed-and-dangerous/